A device disclosed in Patent Document 1 mentioned below is known as an example of the vehicle drive device described above. In the device according to Patent Document 1, an engagement element provided in a speed change mechanism is disengaged to control the speed change mechanism into a neutral state in which transfer of a drive force between an input member and an output member is not performed, and to drive wheels using the drive force of a rotary electric machine.
However, it is assumed that during travel in the neutral state, the operating state of an actuator for the engagement element which has been controlled so as to be disengaged may be unintentionally varied because of erroneous operation of a control device or a failure of the actuator. In this case, it is assumed that torque matching torque transferred through the engagement element corresponding to the actuator, the operating state of which has been varied, is transferred from the speed change mechanism to the wheels. In such a case, negative torque (braking torque) may be transferred from the speed change mechanism to the wheels during travel in the neutral state to affect the travel state of the vehicle or give an uncomfortable feeling to a driver.
A device described in Patent Document 2 mentioned below is configured to prevent locking of rotation in a speed change mechanism when a shift speed is established in the speed change mechanism and in the case where an actuator for an engagement element that is not engaged to establish the shift speed is electrically disconnected or short-circuited so that the engagement element is engaged. Specifically, when the total of current values supplied to three actuators (linear solenoid valves) is equal to or more than a threshold, the device according to Patent Document 2 determines that the speed change mechanism is brought into a locked state with the three actuators driven at the same time so that supply of electric power to one of the actuators is blocked.
However, the device according to Patent Document 2 detects a locked state of the speed change mechanism, and may not determine wheel transfer torque transferred because of unintentionally produced transfer torque of the disengagement engagement element during traveling in the neutral state. In addition, the device according to Patent Document 2 makes a determination on the basis of the sum of current values for the plurality of actuators, and therefore may not accurately determine the effect of the current values for the actuators on the wheel transfer torque.